Condensed-Matter Physics & Materials Science Seminar

Power conversion—converting electricity between different levels of voltage and current—forms the vital link between sources of electric power and the loads they serve. Current topics include renewable energy integration to the electrical grid and deployment of energy-efficient technology on the user side, such LED lighting, in which improvement to DC-DC power conversion is sought.Our current project is a collaboration between City College, Columbia University and UC Berkeley to design new dielectric materials for capacitors, explore new methods to fabricate the devices through spin coating and printing, and design new ways to configure the devices into circuit architectures for DC-DC conversion.
In our materials chemistry group, we have developed several distinctive methods to enhance the dielectric performance of thin films built from uniform, ABO3 type nanocrystals. Nanocrystal films are appealing from both the viewpoint of fabrication and tailorable physical properties. However, a self assembled nanocrystal film exhibits porosity that is detrimental to dielectric performance, especially in terms of frequency dependent loss. Here we elaborate on the models for assessing dielectric performance and outline methods for preparing dense and high dielectric performance nanocrystal thin films (stable dielectric constant and low dielectric loss). The approaches advocated here involve precise methods to prepare films, reliant on evaporatively driven assembly, of perovskite BaxSr1-xTiO3 (x = 0.7, referred to as BST) nanoparticles with uniform size distributions in the 7-30 nm size range, coupled with the use of low molecular weight precursor chemistry (such as furfural alcohol as a monomer, or inorganic high k precursor solution) that can infiltrate porous nanocrystal thin films post assembly. The interparticle void space (low k dielectric volume fraction) is minimized in this fashion, while simultaneously promoting interparticle connectivity and maximizing th